Actually MacOS 8.1 isn't a half-bad OS, and your hardware is going to have a rough time pushing OS X around.
Biggest problem you're going to have with MacOS 8.1 is that the world has moved on. Figure that 70% of the Mac sw available for download is going to be MacOS X binaries (useless to you under OS 8) and that, of the remaining 30%, 2/3 of it will require MacOS 9.2 or 9.0 or 8.6 as minimum operating systems.
I would advise upgrading to MacOS 9, your hardware won't whimper about 9.x the way it will about OS X. (You can also upgrade your hardware but I don't know if you feel like dumping money into this machine. With enough RAM and, ideally, a G4 processor upgrade, you can run OS X nicely)
But if you really want to run 8.1 --
Your browser: iCab. Nothing else that will run under 8.1 is even remotely up to date, nor easy to find. There is a Classic build of Mozilla that's more compatible with what's out there on the web, but I don't believe it will run under 8.1
http://www.icab.de <-- you need version 2.9.8
Places to find other software:
http://www.versiontracker.com isn't bad, you can browse strictly "MacOS 8-9" applications and ignore all the OS X stuff you can't use. Check each program for minimum operating system before downloading anything, remember that more often than not you'll see a minimum OS higher than what you're running.
You will need Stuffit Expander to decompress archived files.
Here is a live link to version 6.5, which will run under MacOS 8.1. Incidentally, that live link goes to the MIT hyperarchive of the old Info-Mac archive:
http://hyperarchive.lcs.mit.edu/HyperArchive/Archive/cmp/stuffIt-lite-65.hqx
Because Info-Mac used to be comprehensive but then stopped getting updated about 4 years ago, it's a gold mine for older versions of freeware and shareware software where the current version won't run under your OS.